This invention relates to a magnetic recording head for forming a magnetic latent image on a magnetic recording medium. More particularly it relates to a thermal and magnetic writing recording head which, while a magnetization pattern is being applied, selectively heats recording regions or non-recording regions consequently the magnetization pattern at the heated positions differs from that at other positions, whereby the magnetic latent image of a picture to be recorded is formed on a magnetic recording medium.
A magnetic recording device of this type is referred to as being "magnetographic", and employs a magnetic head for writing data on a magnetic recording medium.
Heretofore, the following methods have been employed in the process of forming magnetic latent images by magnetography. In a first method, an AC current modulated with an image signal is applied to a magnetic head which is in close contact with a belt-shaped magnetic recording medium, to form a magnetic latent image on the recording medium. In a second method, a DC current modulated with an image signal is applied to heat-generating elements which are in close contact with a magnetic recording medium having a relatively low magnetic transformation point, to form a magnetic latent image on the recording medium. In the second method, an AC magnetic field is applied to portions of the magnetic recording medium heated to temperatures higher than the magnetic transformation point. However, the employment of the magnetic head is disadvantageous for the following reasons: In the case where one magnetic head is used to write data, it takes a relatively long period of time to form the latent image. Even if a method is employed in which a drum-shaped magnetic recording medium is rotated at high speed to write data, it still takes about thirty seconds to write data on a sheet of "A4" size. Since, in this case, the drum must be turned at high speed and an auxiliary scanning operation is required, the device necessarily becomes intricate in construction and high in manufacturing cost. On the other hand, a so-called "multi-magnetic-head" long enough to cover "A4" or "B4" sizes, in which a number of magnetic heads are juxtaposed to write data with a density of about ten lines/mm for every line might be used. However, in this case, it is necessary to arrange 1,000 to 2,000 magnetic heads in a line, and therefore it is considerably more difficult to manufacture the multi-magnetic head.
A magnetic recording device in which particular positions on a magnetic recording medium having a uniform magnetization pattern uses a thermal head for selectively and locally heating the medium to a temperature higher than the transformation point (the Curie point or compensation point). This forms a magnetic latent image on the magnetic recording medium. The device uses a bias magnetic field as a means for imparting the uniform magnetization pattern to the magnetic recording medium and a thermal head as a heating means. In conventional magnetographic devices, these means are provided separately, which has made the device bulky and intricate.
In conventional devices, the bias magnetic field applying means confronts the thermal head on opposite sides of the magnetic recording medium. Accordingly, either the bias magnetic field applying means or the thermal head confronts directly the base layer (generally a plastic film) of the medium. If the thickness of the base layer is taken into account, either the bias magnetic field or heat from the thermal head as the case may be will not be directly applied to the recording medium. As a result of which the printed image will be low in density, i.e., less than 1.0.
In order to increase the recording speed in the first method described above, it is essential to drive a number of recording heads juxtaposed over the recording medium. The magnetic head array cannot be manufactured without a considerably intricate and delicate machining technique. Such a magnetic head array is considerably expensive to manufacture. Thus, the first method is not practical.
One example of a process of forming a magnetic latent image according to the second method will be described with reference to FIG. 1. A magnetic recording medium 1 having a relatively low magnetic transformation point, is provided in the form of a belt supported by a base layer 2. A heat-generating element array 3 has a heat-generating section 4 which is run in close contact with the recording medium. Current signals are applied to the heat-generating element array 3 according to image data, so as to heat the recording medium 1 to temperatures higher than the magnetic transformation point. In this operation, AC current flows in a winding 6, so that an AC magnetic field is formed in the gap of a magnetic head core 5. Therefore, while the magnetic recording medium 1 is being cooled down, the heated portions of the recording medium are subjected to thermal residual magnetization, whereby the AC magnetic field is left in the form of a magnetization pattern in the recording medium. The magnetic recording medium, which is essential for practicing the method, may be formed with CrO.sub.2 for instance.
The Curie point of CrO.sub.2 is about 130.degree. C., which can be readily reached by the heat-generating element array. In general, a plastic material is employed as a base layer for the CrO.sub.2 recording medium. The plastic material is thermally deformed at temperatures around 130.degree. C. Therefore, if the recording medium is used repeatedly, the thermal deformation appears as noise in the process of development with magnetic toner. In addition, CrO.sub.2 is, in general, dispersed in a binder, to prepre a coating type recording medium, and therefor its magnetization density is not high. Accordingly, the developing capability thereof is not sufficient even when saturated recording is employed.